Mineral fillers such as calcium carbonate are commonly added to a plastic material (such as unsaturated polyester resins) to provide reinforcement, increase hardness and to lower overall formulation cost. Other mineral fillers such as alumina trihydrate, which endothermically decompose upon heating to liberate water, are known to have a flame retardant effect in plastic materials such as unsaturated polyester composites. However, adding a significant amount of filler the overall viscosity of the system generally increases. Dispersing agents are commonly used to wet out the dry filler during mixing, reduce the viscosity and make the formulation more workable. Phosphate esters are highly effective dispersing agents but they cannot be used in hand- and spray-lay-up applications due to interference with the curing mechanism.
A number of references disclose dispersants for media such as plastics are summarised below.
U.S. Pat. No. 5,300,255 discloses dispersants containing a polyester derived from a hydroxycarboxylic acid with not more than 8 carbon atoms reacted with phosphorus pentoxide or sulphuric acid. The dispersants are useful in non-polar media, such as aromatic solvents and plastics.
U.S. Pat. No. 5,130,463 discloses dispersants containing a polyether/polyester derived from ε-caprolactone reacted with polyphosphoric acid.
U.S. Pat. No. 6,051,627 discloses dispersants including a polyether derived from ethylene oxide and propylene oxide reacted with polyphosphoric acid.
U.S. Pat. No. 4,281,071 discloses the use of an organo-phosphite for viscosity reduction of filled unsaturated polyester resin compositions.
Non-phosphate dispersants are disclosed in U.S. Pat. Nos. 3,332,793. 3,332,793 discloses suspending agents based upon carboxylic acid-terminated polyether/polyester chains subsequently reacted with a polyamine.
A number of documents disclose methoxy polyethylene glycol esters of polyacrylic acids and their use as dispersants.
EP 2 065 403 A discloses a process for making methoxy polyethylene glycol esters of polyacrylic acid, and their salts, as dispersants for gypsum, cement, and pigments in aqueous systems.
EP 1 061 089 A discloses methoxy polyethyleneglycol esters of polyacrylic acid, modified with organic amines, as cement super-plasticisers.
U.S. Pat. No. 5,840,114 discloses a methoxy polyethyleneglycol ester and methoxy polyethyleneglycol amide of a polycarboxylic acid prepared by direct esterification/amidation.
U.S. Pat. No. 5,476,885 discloses methoxy polyethyleneglycol esters of poly(meth)acrylic acids prepared from the reaction of the methoxy polyethyleneglycol with (meth)acrylic acid.
German Patent DE 3 325 738 discloses products made by the direct esterification of polyacrylic acid with C16-18 alcohol ethoxylates.